Fuel injection valve

ABSTRACT

In a fuel injection valve having a valve body, which contains a movable injector needle, having an actuating part, which supports the injector needle and communicates with a control pressure chamber, and having a compensation chamber, which communicates with a compensation piston, a closing force that counteracts a dynamic opening force should be reliably exerted on the actuating part. To this end, a spring element that exerts a compensating force on the injector needle is disposed between the injector needle and the compensation piston.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 USC 371 application of PCT/DE 00/02734 filed onAug. 12, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a fuel injection valve having a valve body,which contains a movable injector needle, an having actuating part,which supports the injector needle and communicates with a controlpressure chamber, and having a compensation chamber, which communicateswith a compensation piston.

2. Description of the Prior Art

A fuel injection valve of the type with which this invention isconcerned has been disclosed by DE 197 27 896 A1. In this known valve,the compensation chamber is used to compensate for an opening forcewhich acts on the injector needle after it opens. This occurs becausewhen the injector needle lifts up from its valve seat, an additionalarea is acted on by high-pressure so that forces that increase up to alimit value act on the injector needle in the opening direction. Inorder to compensate for the opening force, a compensating force whichcounteracts the opening force is produced in the compensation chamber.In the known fuel injection valve, the actuating part is provided withan annular shoulder that is disposed inside the compensation chamber.The compensation chamber is filled with a fluid, for example the fuel tobe injected, so that a hydraulic chamber is produced which is closed butwhose volume can be displaced by the movement of the compensationpiston. When the injector needle is open, the actuating part is pushedfurther into the compensation chamber so that because of the annularshoulder, the fuel in the compensation chamber is displaced. Thisdisplacement initially produces a pressure increase in the compensationchamber due to the rigidity of the hydraulic volume and the elasticproperties of the fuel contained therein. After this initial pressureincrease, the volume of the compensation chamber is displaced as aresult of which the compensation piston is also moved. The forcecounteracting this movement acts as a closing force on the actuatingmember. The progression and amount of closing force can be adjusted bymeans of the volume of the compensation chamber and the embodiment andimpingement of the compensation piston.

SUMMARY OF THE INVENTION

The fuel injection valve according to the invention has the advantagethat the compensating force can be produced in a simpler manner withoutthe need for a hydraulic chamber between the actuating part and thecompensation piston. In particular, this eliminates all the problemsthat stem from the use of a hydraulic fluid, namely supplying thehydraulic fluid and preventing unintentional escape of the hydraulicfluid.

According to a preferred embodiment of the invention, the spring elementis constituted by at least one Belleville washer, or disk spring. A diskspring or a disk spring packet has the advantage that it produces acharacteristic curve which, in a particular range, demonstrates a verysmall increase in the spring force over the spring travel. As a result,an essentially constant closing force can be produced.

According to a preferred embodiment of the invention, the compensationpiston is disposed concentric to the longitudinal axis of the actuatingpart. This produces a particularly compact design of the fuel injectionvalve.

According to one variant, the compensation piston is annular andencompasses the actuating part, the compensation chamber is an annularchamber which encompasses the actuating part and is closed at one end bythe compensation piston, and the actuating part is provided with acollar which supports the spring. This embodiment produces a design ofthe fuel injection valve that is very compact in the axial direction.

According to another variant, at the end remote from the injectorneedle, the actuating part is provided with a support disk, whichsupports the spring, and the support disk is disposed opposite from thecompensation piston which, at its end remote from the injector needle,is provided with an extension that closes one end of the compensationchamber. This embodiment produces a design of the fuel injection valvethat is slender in the radial direction.

Preferably, two stops for the compensation piston are embodied on thevalve body, which determine the end positions of the compensationpiston. Consequently, in the event of an excessively high or excessivelylow pressure in the compensation volume, there are preset positions thecompensation piston which assure a correct operation of the fuelinjection valve.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below with reference to two preferredembodiments that are shown in the accompanying drawings, in which:

FIG. 1 is a schematic sectional view of a first embodiment of a fuelinjection valve according to the invention;

FIG. 2 is a schematic sectional view of a second embodiment of a fuelinjection valve according to the invention; and

FIG. 3 shows the progression of the dynamic opening force for a fuelinjection valve according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a 2/2-way fuel injection valve for a so-called “commonrail” injection system. The injection valve has a valve body 10 whichcontains a movable injector needle 12. The injector needle cooperateswith a valve seat 14 in order to control the injection of fuel, which issupplied via a supply line 16, into a cylinder of an internal combustionengine, not shown.

An actuating part 18 is supported on the injector needle 12 and its endface remote from the injector needle 12 closes a control pressurechamber 20. An annular leakage collecting chamber 17 is embodied in thevalve body 10 and encompasses the actuating part 18. A feed line 22connected to the supply line 16 leads to the control pressure chamber 20and contains an inlet throttle. An outlet line 24 leads from the controlpressure chamber 20, has an outlet throttle disposed in it, and iscontrolled by a control valve 26.

When the control valve 26 is closed, the fuel pressure prevailing in thecontrol pressure chamber 20 produces a closing force that is greaterthan an opening force produced by the fuel in the vicinity of theinjector needle 12. The injector needle 12 consequently rests againstthe valve seat 14 and no fuel is injected. When the control valve 26 isopen, the escaping fuel causes the pressure in the control pressurechamber to decrease so that the opening force produced in the vicinityof the injector needle 12 becomes greater than the closing forceproduced in the vicinity of the control pressure chamber 20.Consequently, the injector needle 12 can lift up from the valve seat 14and fuel is injected. When the control valve 26 is closed again, aclosing force is once again exerted on the actuating member 18 whichcauses the injector needle 12 to close.

When the injector needle 12 lifts up from the valve seat 14, anadditional area is produced that is acted on by the fuel pressure, as aresult of which an additional opening force is produced. This openingforce has a dynamic progression and is shown by way of example in FIG. 3for four different fuel pressures in the common rail injection system bythe curves 1, 2, 3, and 4. In order to counteract this additionalopening force, a compensation system is provided which exerts acompensating force on the actuating member.

The compensation system is comprised of an annular compensation chamber30, which encompasses the actuating member 18 and is closed at one endby an annular compensation piston 32. The compensation chamber 30communicates with the supply line 16 via a feed line 34.

The actuating part 18 is provided with a collar 36 which is disposed ina spring chamber 38. A spring disk packet 40 is disposed between thecollar 36 and the end face of the compensation piston 32 oriented towardthe injector needle 12. The spring disk packet has a spring rigidity ofapproximately 4 N per micrometer.

When the injector needle 12 opens, the spring disk packet 40 isinitially compressed by means of the collar 36. This produces acompensating force which increases sharply as a function of the springrigidity of the spring disk packet 40. In FIG. 3, this is shown on theleft side of the curve A for the compensating force.

As soon as a predetermined amount of force is produced, the compensationpiston 32 moves in the compensation chamber counter to the compressiveforce produced by the fuel in the compensation chamber 30. The movementof the piston 32 assures that the compensating force is kept at aconstant level. This is depicted by the horizontal part of the curve Ain FIG. 3. On the whole, a compensating force is thus produced whichdepends on the pressure in the supply line 16 and compensates for thedynamic opening force.

FIG. 2 shows a second embodiment of a fuel injection valve according tothe invention. It differs from the first embodiment in terms of theembodiment of the compensation system.

The actuating part 18 is provided with a support disk 50 on which thedisk spring 40 rests. The compensation piston 32, which is provided withan extension 52, is disposed opposite the support disk 50. Thisextension 52 closes one end of the compensation chamber 30.

The function of the compensation system corresponds to that of thecompensation system in the first embodiment.

One advantage resulting from the use of the mechanical spring 40 is thatthere are no losses over time during the opening of the valve.Furthermore, during the opening of the injector needle 12, potentialenergy which is needed later for the closing is temporarily stored inthe spring.

Valve body 10 has two stops 60, 62 embodied in it which determine theend positions for the compensation piston 32. The stops assure that itis possible for the compensation system to function even when there isan excessively high or excessively low pressure in the supply line 16.

The foregoing relates to a preferred exemplary embodiment of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

We claim:
 1. In a fuel injection valve having a valve body (10), whichcontains a movable injector needle (12), having an actuating part (18),which supports the injector needle (12) and which delimits a controlpressure chamber (20) having an inlet and an outlet line of pressurizedfuel and a control valve in one of them to change the effective pressurein the control chamber for actuation of the actuating part of theinjector needle, said fuel injection valve having further a compensationchamber (30) exposed to the pressurized fuel and delimited by acompensation piston (32), which further acts under the pressure of thecompensation chamber via a spring element (40) on the injector needle inits closing direction generating a compensation force on that needle. 2.The fuel injection valve according to claim 1, wherein the springelement is constituted by at least one spring disk (40).
 3. The fuelinjection valve according to claim 2, wherein the compensation piston(32) is disposed concentric to the longitudinal axis of the actuatingpart (18).
 4. The fuel injection valve according to claim 3, wherein thecompensation piston (32) is annular and encompasses the actuating part(18), that the compensation chamber (30) is an annular chamber whichencompasses the actuating part (18) and is closed at one end by thecompensation piston (32), and that the actuating part (18) is providedwith a collar (36) which supports the spring element.
 5. The fuelinjection valve according to claim 3, wherein on the end remote from theinjector needle (12), the actuating part (18) is provided with a supportdisk (50) which supports the spring element (40), and that the supportdisk (50) is disposed opposite from the compensation piston (32) which,on its end remote from the injector needle (12), is provided with anextension (52) which closed one end of the compensation chamber (30). 6.The fuel injection valve according to claim 5, wherein two stops (60,62) for the compensation piston (32) are embodied on the valve body(10), which determine the end positions of the compensation piston (32).7. The fuel injection valve according to claim 3, wherein two stops (60,62) for the compensation piston (32) are embodied on the valve body(10), which determine the end positions of the compensation piston (32).8. The fuel injection valve according to claim 2, wherein two stops (60,62) for the compensation piston (32) are embodied on the valve body(10), which determine the end positions of the compensation piston (32).9. The fuel injection valve according to claim 1, wherein thecompensation piston (32) is disposed concentric to the longitudinal axisof the actuating part (18).
 10. The fuel injection valve according toclaim 9, wherein the compensation piston (32) is annular and encompassesthe actuating part (18), that the compensation chamber (30) is anannular chamber which encompasses the actuating part (18) and is closedat one end by the compensation piston (32), and that the actuating part(18) is provided with a collar (36) which supports the spring element.11. The fuel injection valve according to claim 10, wherein two stops(60, 62) for the compensation piston (32) are embodied on the valve body(10), which determine the end positions of the compensation piston (32).12. The fuel injection valve according to claim 9, wherein on the endremote from the injector needle (12), the actuating part (18) isprovided with a support disk (50) which supports the spring element(40), and that the support disk (50) is disposed opposite from thecompensation piston (32) which, on its end remote from the injectorneedle (12), is provided with an extension (52) which closed one end ofthe compensation chamber (30).
 13. The fuel injection valve according toclaim 12, wherein two stops (60, 62) for the compensation piston (32)are embodied on the valve body (10), which determine the end positionsof the compensation piston (32).
 14. The fuel injection valve accordingto claim 9, wherein two stops (60, 62) for the compensation piston (32)are embodied on the valve body (10), which determine the end positionsof the compensation piston (32).
 15. The fuel injection valve accordingto claim 1, wherein two stops (60, 62) for the compensation piston (32)are embodied on the valve body (10), which determine the end positionsof the compensation piston (32).